Forty children with and 40 children without Attention deficit Hyperactivity Disorder (ADHD) receive Docosahexaenoic Acid (DHA) and Eicosapentaenoic Acid (EPA) or placebo via a dietary intervention. Cognitive control functions are measured with functional Magnetic Resonance Imaging (MRI) before and after the intervention. Behavioural change is monitored with behavioural scales.